JPH07206781A - Production of dimethyl carbonate - Google Patents

Abstract

PURPOSE: To obtain dimethyl carbonate useful as a material for the synthesis of an aromatic polycarbonate, or the like, efficiently, in high purity and in high yield by reacting methanol, carbon monoxide and oxygen in the presence of a copper compound.

CONSTITUTION: Dimethyl carbonate is obtained by reacting methanol 1, carbon monoxide 2, and oxygen 3 in the presence of Cu (I) and Cu (II) compounds, and a molten Cu salt 7 of a mixture thereof, or the like, at 120 to 300°C and 1 to 70 bar in a reaction distillation device A, while separating and eliminating the water 9 generated in the reaction at least partially from the stripping region or the bottom phase of the reaction distillation device A.

COPYRIGHT: (C)1995,JPO

Description

Detailed Description of the Invention

The present invention relates to dimethyl carbonate (DM) by oxycarbonylation of methanol in the presence of Cu salt.
C) relates to an improved production method.

Dimethyl carbonate is a less toxic intermediate,
In many reactions toxic intermediates can be substituted, such as phosgene or dimethyl sulfate. This material is also not corrosive. Its use does not produce environmentally damaging by-products.

An example of this type of reaction of dimethyl carbonate is the production of urethanes from aliphatic or aromatic amines,
The urethane can subsequently be cleaved to give the corresponding isocyanate. Dimethyl carbonate can also be replaced by dimethyl sulfate in the quaternization of amines or in the methylation of phenols or of naphthols. Dimethyl carbonate can also be added to automotive fuels, for example in place of lead compounds, to improve octane number. This importance of dimethyl carbonate has facilitated the search for technically simple and environmentally friendly manufacturing processes that are suitable for large volumes, produce no significant by-products or are associated with material cycling.

There are various production processes, both small-scale and industrially tested, for producing dimethyl carbonate. Manufacturing routes based on the catalytic reaction of methanol with carbon monoxide and oxygen according to the following equations have been vigorously studied by various groups of researchers:

[0005]

[Equation 1]

The copper compound thus acting as a catalyst has been used in the form of various copper salts. JP-45 /
11129 (1970), copper chloride (I
The use of I) as a catalyst gives unsatisfactory selectivity. A particular problem is that due to its high volatility it tends to be evenly distributed throughout the manufacturing plant and results from the production of relatively large amounts of methyl chloride which can lead to corrosion in virtually all plants. .

Better selectivity is obtained by using organic complexing agents (DE-A2110194).
However, this poses the problem of separating off the catalyst salts, which are partly dissolved in the reaction mixture but whose main part is present as a suspension.

Particularly problematic is the reaction of this reaction with DE-
This is a case where it is performed according to A2743690. In this case, the catalyst salt is virtually completely insoluble in the reaction mixture and is merely suspended. These salts have to be transported through the reaction zone, through a cooling device and after the reaction have to be separated off mechanically, for example by means of centrifugation. Besides the already mentioned corrosion, it causes erosion, poor heat transfer, and plugging and crusting.

In order to avoid these deficiencies in the catalytic circuit, it is necessary to keep the catalyst salt in suspended form in the reactor,
Further, it is proposed that methanol, CO and oxygen are metered into the reactor, and the generated dialkyl carbonate and water produced by the reaction are distilled out from the reactor together with excess methanol used (EP0413215).
A2). Here, the liquid reaction medium basically consists of methanol to be reacted (EP041321).
5, page 3, line 52), therefore methanol vs. C
The molar ratio of u salt is extremely high (preferably 1: 0.01-
0.05). This method has the disadvantage of a relatively low reaction rate. The need to set a low dimethyl carbonate concentration is also a problem here. This reaction is carried out at a high system pressure and the above conditions are not easy because the solubility of dimethyl carbonate and water in the reaction medium consisting essentially of methanol is very high. This means that the separate removal of dimethyl carbonate and water must be forced by a relatively large amount of inert gas or gaseous methanol.

In a relatively new process according to DE-A-4138755 it has been shown that the use of Cu compounds in the form of molten salts at 120 to 300 ° C. can considerably increase the reaction rate of the oxycarbonylation of methanol. Has been done. The special advantages of this method are:
It is of value if the water content of the reaction mixture can be kept low (patent application P43 of 30 July 1993).
25651.1). At 120 ° C. to 300 ° C. and 1 to 70 bar in the presence of molten Cu salt, in a reactive distillation apparatus, the water formed during the reaction is at least partially separated off from the stripper zone or bottom phase of this reactive distillation apparatus. An improved process has now been found for producing dimethyl carbonate by the reaction of methanol with carbon monoxide and oxygen in the presence of a copper compound, comprising carrying out the reaction in such a manner.

In this method, the water produced by the reaction can be removed from the reaction system and the Cu salt-containing melt is present in the water present as well as in any organic matter such as dimethyl carbonate, methanol or in the system. It can be recycled to the reactive distillation apparatus after separating and removing other chemical species that are present.

In this method, the water content of the reaction mixture is controlled and reduced to a low value. The process is generally carried out with a water content of less than 10%, but it is advantageous to keep the water concentration in the reaction mixture below 6% by weight. It is particularly advantageous to operate the reaction with a valency of less than 3% by weight in order to obtain a high conversion as well as a very high selectivity. In a particular embodiment, the water content is 1
It is less than%.

The method according to the invention is preferably carried out with a salt melt containing Cu salts, suitable Cu salts being C
u (I) and Cu (II) compounds, and mixtures thereof. In principle, all known Cu salts are suitable, provided that the salt is only soluble to some extent in the salt melt.

In addition to halides such as chlorides or bromides, cyanides, rhodanides, sulfates, nitrates, carbonates, acetates, formates, oxalates, and alkoxides such as methoxycopper chloride are also suitable salts. Is. Cu can also be used in the form of complex compounds such as acetylacetonate, or Cu-N complexes such as Cu-pyridine complexes or Cu-dipyridyl complexes.

The salt melt is generally prepared from a mixture of salts having a low melting point, ie forming a eutectic mixture. Therefore, it is advantageous to use a proportion of salt that corresponds to the composition of the eutectic mixture. This type of eutectic mixture is C
It can be formed from a mixture of the u salt and one other salt, or a Cu salt and a plurality of other salts.

Thus, in principle, besides the Cu salt, it is chemically inert for the purposes of the invention, or else catalytically active, ie the activation energy is reduced with respect to the oxycarbonylation of alcohols. It is possible to use all salts which make it possible. In addition to Cu salts, a wide range of salts or salt-like compounds are used here. Mixtures of Cu salts and salt-like compounds of this kind are generally used. The use of halides of the first to third main group or subgroups is preferred. Particularly suitable salts are alkali metal chlorides, such as NaCl or KCl, or alkaline earth metal chlorides, such as CaCl ₂ or MgCl ₂ , and ZnCl ₂ . However, it is also possible to use less common compounds, for example chlorides of thallium, indium or gallium.

A suitable melt is, for example, one which consists of various proportions of Cu (I) chloride and KCl. The mixture generally selected has a high proportion, for example CU chloride.
It has a weight ratio of (I) to KCl of 60 to 75:40 to 25 Cu compound.

The reaction temperature is generally about 120 ° C. to 3 °
00 ° C., preferably 120 ° C. to 180 ° C .; typical reaction temperatures 140 ° C. to 170 ° C., advantageously 1
45 ° C to 160 ° C.

The reaction can also be carried out at atmospheric pressure, but in order to achieve a sufficiently high reaction rate, the reaction can be carried out at a higher pressure, for example 5 to 70 bar, preferably 10 to 50 bar. Particular preference is given to carrying out at 12 to 22 bar.

The molar ratio of the reaction components used is important with respect to the reaction rate and the selectivity of the reaction. If these relationships are not observed, there are by-product products such as dimethyl acetal of formaldehyde, or methyl chloride, which causes special problems.

This ratio is generally chosen to use a molar excess of methanol over carbon monoxide and thus an excess of carbon monoxide over oxygen, but at most a molar amount of CO and O _2. . Therefore, 1 mole ratio CO and O ₂ alkanol selected: 1-0.
01: 1-0.01, preferably 1: 0.5-0.0
2: 0.3-0.02. This gives, for example, 1
Conversions of 0 to 50% methanol and 10 to 80% CO are obtained. Oxygen is generally completely reacted. Of course, it is necessary to pay attention to the explosion limit when selecting the amount used. If desired, it is also possible to carry out the reaction in the presence of an inert gas such as N ₂ or CO ₂ .

Oxygen can be used, for example, in the form of atmospheric air or O ₂ -enriched air.

Unreacted amounts of methanol and CO can be recycled after separating off the dimethyl carbonate and water, and optionally CO ₂ .

The process according to the invention can be carried out batchwise, but is particularly suitable for the continuous automatic production of dimethyl carbonate. A suitable reactive distillation apparatus is a conventional distillation column into which the melt containing the Cu salt is metered in under the top zone, together with the reflux of the column and optionally methanol used, optionally in the central region of the column. Flow downwards over the internal parts or packings of the column having a gas mixture containing oxygen and CO in the presence of an inert gas introduced into the column, such as N ₂ or CO _2. It flows toward things.

The residence time of the reaction gas in the melt is generally
It is sufficient to achieve sufficient conversion to dimethyl carbonate with conventional distillation equipment. In this method, 0.5
It is possible to easily set a dwell time of to 500 seconds. If desired, the amount of liquid phase can be increased to further extend the residence time.

In addition to conventional packing, conventional column plates can be used, but it is also possible to raise the downflow weir in the plate column to set the desired residence time. The reactive distillation apparatus used can also be a single stage or a multi-stage bubble column, optionally with stirring.

The liquid flowing down below the entry points of the reaction gases CO and O ₂ contains, in addition to the Cu salt, also the water produced by the reaction and possibly dimethyl carbonate. Depending on the pressure and temperature conditions and the reflux ratio, the amount of dimethyl carbonate flowing towards the bottom with the melt and the water produced by the reaction can be varied or fixed. These reaction conditions in the reactive distillation apparatus can also be chosen in such a way that the DMC formed during the reaction is mostly taken off at the top with methanol. But,
These conditions can also be chosen in such a way that the DMC is taken off at the bottom with the melt and the water produced by the reaction. Subsequently, the water produced by the reaction from the bottom phase and, if appropriate, the DMC are removed, for example by pressure relief. The melt is refluxed into the reaction zone, optionally with fresh methanol.

Water produced by the reaction is optionally removed from the system by distilling off organic matter such as DMC.

In the zone above the molten salt influx point of the reactive distillation apparatus, methanol and possibly dimethyl carbonate are distilled off together with a small amount of volatile by-products such as formaldehyde dimethyl acetal.

After condensation, the top product is optionally partially recycled to the reactive distillation apparatus. The part of the condensate which is not to be recycled is removed from the column. Pure DMC was isolated from the material removed from this column by known techniques,
Methanol is recycled to the reaction zone.

The heat of reaction generated in the reaction zone is removed using a vaporizing reactant.

Any mixture of methanol and dimethyl carbonate obtained in the work-up of the reaction mixture can be recycled to the reaction zone as a mixture and used as a source of methanol.

In this process, the methanol introduced into the reaction zone may already contain a relatively large amount of dimethyl carbonate, which has a composition corresponding to, for example, a methanol / dimethyl carbonate azeotrope. However, it may also contain higher amounts of DMC.

A particular advantage of the process according to the invention is that the reaction mixture obtained is, for example, 10 to 90% by weight,
It preferably has a high dimethyl carbonate content of 50 to 70% by weight, which makes it possible to isolate pure dimethyl carbonate in a particularly simple and economical manner.

Suitable materials for constructing the reactive distillation apparatus are, for example, corrosion-resistant stainless steel, enameled steel,
It is a special metal such as glass, graphite, or tantalum.

The process according to the invention can also be carried out industrially on a large scale. Here, for example, as shown in FIG. 1, a reactive distillation apparatus (A) can be used, and methanol (1) is passed through this apparatus (A) to salt melt (7).
And with a DMC / methanol azeotrope (11) countercurrently to a gas stream with a circulating gas (4) of CO (2) and O ₂ (3).

Water (9) produced by the reaction is distilled off from the bottom of the column of the apparatus (A) after releasing the pressure. The melt from which water has been removed is recirculated to the column (A).

At the top of column (A), the condensed phase split stream is returned to the column after condensation. Other about 60% DMC
The split stream containing (the remainder is methanol) flows into the azeotropic column (B), from which dimethylformal (10) is withdrawn at 10 bar at the top. The bottom effluent of the azeotropic column (B) flows into a dimethyl carbonate purification column (C) from which pure dimethyl carbonate (8) is obtained as an outlet stream near the bottom. The top product of the DMC purification column (C) consists essentially of an azeotrope of dimethyl carbonate and methanol and is recycled to the reaction zone with the salt melt.

The non-condensable component (4) from the reactive distillation unit (A) is recycled to the reaction zone using a compressor. The split stream (5) of the circulating gas is discharged to remove the inert gas.

Further, the method of the present invention can be carried out as shown in FIG. 2 as follows. Methanol (1) is introduced into the reactive distillation apparatus (A) together with the melt (7). This flow flows downwards through the internal parts of the column, and the mixture of reaction gas O ₂ (3) and CO (2) flows upwards, countercurrently with the circulating gas (4). Below the reaction zone, a mixture of molten salt, water and dimethyl carbonate flows to the bottom of the reactive distillation column, where this product stream containing salt melt, water and dimethyl carbonate is withdrawn. Water and dimethyl carbonate are distilled off from this substance discharged at the bottom and fractionated in a water separation column (B), where water (9) is obtained at the bottom.

At the top, the water / dimethyl carbonate azeotrope is distilled off. After phase separation, the separated water is allowed to flow back through the column. The upper organic phase essentially contains dimethyl carbonate, which is removed from the DMC purification column (C) as an outlet stream near the bottom (8).

Above the reaction zone of the reactive distillation apparatus (A),
The material distilled off consists essentially of methanol and volatile by-products such as formaldehyde dimethyl acetal. The condensate is basically returned as a product stream (6) as reflux to the reactive distillation column (A). In order to remove the volatile by-products from the system, the condensate substream has a smaller substream (purge, 10) discharged. The non-condensable components of the top product (4) are recycled to the reaction zone using a compressor. In order to remove the inert gas, a diversion (5) is made from this circulating gas.
Is discharged.

[0043]

[Table 1]

[0044]

[Table 2]

The main features and aspects of the present invention are as follows.

1. In a reactive distillation apparatus in the presence of molten Cu salt at 120 ° C. to 300 ° C., 1 to 70 bar, the water formed during the reaction is at least partially separated off from the stripping zone or bottom phase of this reactive distillation apparatus. A method for producing dimethyl carbonate from methanol, carbon monoxide and oxygen in the presence of a copper compound, which comprises carrying out the reaction by such a method.

2. Process according to claim 1, characterized in that the water content in the reaction zone is maintained at a value of less than 6% by weight, preferably less than 3% by weight, very particularly preferably less than 1% by weight.

3. 2. The method according to 1, characterized in that a melt of Cu (I) chloride and KCl is used.

4. CuCl: KCl = 60 to 75:
4. The method according to 3, wherein the weight ratio is set to 40 to 25.

5. Alkanol: CO: O ₂ = 1: 1-
0.01: 1-0.01, preferably 1: 0.5-0.
The method according to 1, wherein the molar ratio is set to 02: 0.3-0.02.

6. 1-5, wherein the water produced by the reaction is taken out from the mixture at the bottom of the reactive distillation apparatus by distillation together with the produced dimethyl carbonate, and the distillate thus obtained is separated into water and dimethyl carbonate. The method described in any of.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a large-scale reactive distillation column device that can be industrially used.

FIG. 2 is an explanatory diagram showing another aspect of the present invention.

Front page continuation (72) Inventor Helmut Baltmann Germany 51373 Lef Elkusen Henry-Tay-V-Betaininger-Schütlerse 15 (72) Inventor Kaspar Hallenberger Germany 51375 Lef Erkusen Binsent -Ban-Gotsho-Syutrase 44 (72) Inventor Bolfram Bagner Germany 41540 Dormagen Zuijihishi Utrase 9 (72) Inventor Hans-Joachim Trenkuner Germany 51375 Lef Erkusen Andersiyu Tyne Liyutschyu 30

Claims (1)

[Claims] 1. 120 ° C. to 3 in the presence of molten Cu salt
It is possible to carry out the reaction in a reactive distillation apparatus at 00 ° C., 1 to 70 bar, in such a way that the water formed during the reaction is at least partially separated off from the stripping zone or bottom phase of the reactive distillation apparatus. A method for producing dimethyl carbonate from methanol, carbon monoxide and oxygen in the presence of a copper compound.